You don't take off the top; you need to take off the side face plate. It's shown on page 32 of the manual in the section on changing the bulb. The face plate is secured with a single screw that is near the front of the machine. After removing the screw, hold the face plate at the bottom. Then pull it to the left and then down and away from the sewing machine.
You should use sewing machine oil. A product like, https://www.amazon.com/Singer-2131E-All-Purpose-Machine/dp/B000YZ1Y06
, will work. It's sometimes easier to dispense the small drop of oil from a pen oil container. Most 3-in-1 oils do not match the needed specifications (clear, very well filtered, low viscosity). You could use white mineral oil but that won't protect against rust as well. The oil for lubricating hair-cutting clippers would work.
I hope this helps.
(In my household, the sewing machine oil is used for lubricating other items when dirt and dark stains are undesirable.)